Flow control apparatus



Dec. 13, 1955 J. J. J. STAUNTON 2,726,670

FLOW CONTROL APPARATUS Filed July 28, 1950 2 Sheets-Sheet l Z 5 HA 4;.

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1955 J. J. J. STAUNTON FLOW CONTROL APPARATUS 2 Sheets-Sheet 2 Filed July 28, 1950 United States Patent FLOW CONTROL APPARATUS John I. J. Staunton, Oak Park, Ill., assignor to Coleman Instruments, Inc., Maywood, Ill., a corporation of Illinois" Application July 28, 1950, Serial No. 176,370

13 Claims. (Cl. 137---93) This invention relates to apparatus for automatically controlling the flow of one liquid into another in response to some preselected condition of the combined solution and more particularly to titration apparatus.

One object of the invention is the provision of apparatus of the above character that is adapted to automatically and positively control the flow of one liquid into the other in response to some preselected condition of the combined solution after the flow of said one liquid has been initiated.

Another object of the invention is the provision of apparatus of the above character that is efiicient, that is reliable, that is rugged, that is accurate, and that has a relatively long life.

Another object of the invention is the provision of apparatus of the above character wherein adjustments may be made to the apparatus without requiring immersion of electrodes.

Another object of the invention is the provision of apparatus of the above character having means for insuring that the component parts of the electrical circuits such as electronic tubes and switch and relay contacts have a relatively long life.

q Another object of the invention is the provision of apparatus of the above character having means for indicating to the operator that the end point has been reached.

Another object of the invention is the provision of apparatus of the above character having means for preventing accidental flow of the titrant due to power line transients or mistakes on the part of the operator such as in handling electrodes and the like before the equipment has been disconnected from the power line.

Another object of the invention is the provision of apparaus of the above character having novel means for preventing the addition of too much titrant to the solution. Another object of the invention is the provision of novel means for providing a reference voltage.

1 Another object of the invention is the provision of ap paratus of the above character having novel valve means. Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in

which---..

. Figure'l is a diagrammatic view of titration apparatus embodying the present invention;

. Fig. 2 is a side elevational view of the valve means in its closed position;

Fig. 3 is a fragmentary view similar to Fig. 2 with the valve means in an open position;

Fig. 4 is a front elevational view of the valve means, and

Fig. 5 is. the wiring diagram of the control apparatus. The invention in its broadest aspects relates to apparatus for .coiitrolling the flow of one liquid into another liquid in response to a preselected condition in the resulting intermixture of liquids. The apparatus chosen to illustrate the invention in Figure 1 is adapted for titration and in general includes valve means 8 connected in a titrant Cir lit

line 9, a cell 10 arranged to be placed in a container 11 having a solution into which the titrant flows, a pH meter 7 connected to the cell 10, and control or instrument means 12 connected between the pH meter 7 and the valve means 8 operative to automatically control the valve means in a predetermined manner in response to a preselected condition in the solution. The pH meter may be of conventional construction. In this embodiment of the invention control means 12 includes an amplifier 13 having its input interconnected with the cell 10 through the pH meter 7 and an output, reference voltage means 14 connected to the input, a valve actuation circuit 16 interconnected with the output and an anticipator circuit 17 disposed between the output of the amplifier 13 and the valve actuation circuit 16 operative to pulsate the output voltage of the amplifier to effect periodic operation of the valve actuation circuit immediately prior to the end point being reached in the solution. These various components are suitably mounted in a casing 15.

The amplifier 13 may be of any of the well-known high grain types having a stable voltage output. One such amplifier is shown in the drawings and includes a power supply 18, voltage regulation means for the power supply, a bleeder resistance 19 connected across the power supply and a pair of electronic tubes 21 and 22. As best seen in Fig. 5 in this embodiment of the invention, the power supply 13 includes a transformer 23 and a rectifier tube 24 having the type designation 5Z4. The primary winding of the transformer 23 is adapted to be connected to a suitable alternating current supply as by conductors 26 and 27. The filaments of the tube 24 are connected across a secondary winding 28 of the transformer 23 by conductors 29 and 31 while the plates of the tube 24 are connected to another secondary winding 32 of the transformer 23 by conductors 33 and 34. A conductor 36 connected to the mid-point on the winding 32 on the transformer 23 forms a negative output conductor of the power supply and a conductor 37 connected to the conductor 31 forms a positive output conductor of the power supply. A condenser 38, rated 16 microfarads, is connected between the conductor 36 and the conductor 37.

The voltage output of the power supply is regulated by a pair of gas tubes 39 and 41 such as VR-l50 tube and a VR tube, respectively, connected in cascade relation across the output conductors 36 and 37. The gas tube 39 is connected to the positive conductor 37 of the power supply by a conductor 42, a resistance 43, rated 450 ohms, and a ballast lamp 44, rated 250 volts, 25 watts, being connected in series in the conductor 42. The gas tube 39 is connected to the negative side of the power supply by a conductor. 46. The gas tube 41 is connected across the tube 39 by conductors 47 and 48 with a resistance 49,

7 rated 3 ohms, being connected in series in the conductor 47 and a ballast lamp 51 being connected in series in the conductor 48.

The tube 39 efiects primary voltage regulation of the output of the power supply and in normal operation this tube receives its current through the ballast lamp 44, the resistance of the lamp 44 and the resistance 43 being of such values that the sum of the current drawn by the tube 39 and the rest of the circuit efiects a voltage drop of about volts across the ballast lamp 44 and a drop of 50 volts across the resistance 43. Thus,

therectifier output voltage which is approximately 350 volts is reduced to 150 volts at the terminals of the rectifier tube 39 which is its normal operating voltage; This tube operates so that if the line voltage of the power supply rises, the tube automatically draws more current and the increased drop across the ballast lamp 44 and across the resistance 43 increases to absorb the Patented Dec. 13, 1955 rise. in supply voltage so that the tube 39 maintains essentially 150 volts across its terminals. The tube 41 is connected so that it is supplied from across the tube 39 after a further drop has been taken through the resistance 49 and the ballast lamp 51, rated 120 volts, 7 watts. The tube 41 operates in the same manner as the tube 39. However, instead of having a large voltage change to absorb it has a small residual. voltage change of only a couple of volts which has been left by the tube 39. Accordingly, the current change through the tube 41 is very small, only enough so that the change in the voltage drop in the resistance 49 and lamp 51 will absorb substantially the remainder of this couple of volts.

The bleeder resistance 19 is connected across the terminals of the tube 41 by conductors 61 and 62. As shown the bleeder resistance includes resistances 63, 64, 66, 67, 68, 69 and 71. In this embodiment of the invention the resistance 63 has a rating of 125 ohms, the resistance 64 has a rating of 34 ohms, the resistance 66 has a rating of 370 ohms, the resistance 67 has a rating of 150. ohms, the resistance 68 has a rating of 1200 ohms, the resistance 69 has a rating of 430 ohms and the resistance 71 has a rating of 1100 ohms.

The tube 21 has its filament connected in series in the bleeder resistance between the resistances 63 and 64. The screen grid of the tube 21 is connected to a juncture between the resistances 66 and 67 by a conductor 72, av three-position selector switch 73 having positions marked Start, Alkali and Acid, respectively, 1

being connected in the conductor 72 as shown. The plate of the tube 21 is connected to the end of the bleeder resistance adjacent the resistance 71 by conductors 74 and 76,. a resistance 77 rated 5 megohms being connected in series in the conductor 74. A selector switch 78' having three positions marked Start, Alkali and Acid is connected in series in the conductor 76. The Acid position of the switch 78 is interconnected with the Start position of the switch 73 by a conductor 79 as shown in Fig. 5. connected to one side of the output of the pH meter 7 by a conductor 82, a resistance 83 rated 1 megohm and a three-position selector switch 85, marked as described hereinbefore, being connected in series in the conductor. A resistance 84, rated 47 megohms, is also connected between the conductor 82 and the conductor 76 or between the grid and plate of the tube 21.

The tube 22 has its filament connected in series in the bleeder resistance between the resistances 67 and 68. The grid of the tube 22 is connected to the plate Reference voltage means An auxiliary bleeder resistance comprising a resistance 96, rated 1500 ohms, a resistance 99, rated 270 ohms, and a resistance 107, rated 15 ohms, is shunted across the regulator tube 41 for purposes of securing the reference voltage against which the pH meter 7 output is balanced, it being understood that the difference is amplified to eiiect actuation of the valve control circuit means. Thus, as shown, the bleeder circuit is interconnected to a three-position selector switch 93, marked Start, Alkali and Acid, by a variable tap 94 on the resistance 96. One end of the resistance 96 is connected to the positive side of the power supply through a conductor 97, the resistance 99, a three-position selector switch 101, marked Start, Alkali and Acid,

a resistance 102, rated 15,000 ohms, a conductor 98, the conductor 74 and the conductor 62. The opposite end of the resistance 96 is connected to the negative side of the power supply through a conductor 103, a three-position selector switch 104, marked Start, Alkali and The grid of the tube 21 is 4 Acid, a conductor 106, the resistance 107, an adjustable tap 108 and a conductor 109. As shown, the Alkali position of the selector switch 93 is connected to the Acid position on the selector switch 85 by a conductor 111a and the conductor 92, the latter being grounded through a conductor 112a and connected to the other side of the output of the pH meter 7. The Alkali position on the selector switch 101 is connected to the Acid" position on the selector switch 104 by a conductor 113. The Acid position on the selector switch 101 is connected to the resistance 107 by a conductor 114. The Start position on the selector switch 85 is connected to the adjustable tap 108 by a conductor 110. As pointed out hereinbefore, the residual variation of the voltage on the tube 41 is corrected by properly balancing the resistance 63 and the resistances 64 and 66, the grid and the screen grid bias of the tube 21 respectively. The actual grid return from the signal of pH meter 7 is through the tap 94 on the resistance 96 and unless some provision is made, the actual grid bias of the tube 21 would be determined by the position of the slider 94 rather than by the resistance 63 and the balance referred to would be lost. Since there is a. current change in the resistance 49 as the voltage across the tube 41 changes a drop can be produced in the resistance 49 which, if properly chosen, can be substantially equal and opposite to the change in the voltage of the tube 41. Thus, the voltage from the negative side of the circuit in the resistance 49 to the valve tap 94- on the resistance 96 remains practically constant. Because of this compensating feature the grid return for the tube 21 can be eliected on the resistance 96.

Anticipator circuit The anticipator circuit 17 is connected to the output of the amplifier and is adapted to provide a pulsating saw tooth voltage on the amplifier circuit output capable of intermittently operating the valve actuation circuit 16 immediately prior to the attainment of some preselected condition in the solution so as to prevent the addition of too much titrant to the solution. The anticipator circuit includes a relaxation type oscillator 111 and a saw tooth voltage generating circuit 112 interconnected with the valve actuation circuit 16 and relay means actuated by the oscillator 111 to efiect energization of the saw tooth voltage generating circuit 112. As shown, the oscillator 111 includes a glow lamp 113 connected in series with a resistance 11'4, rated 56,000 ohms, and shunted by a condenser 115, rated 10 microfarads, and a coil 116 of the relay means. The oscillator 111 is connected across a suitable power supply by a conductor 118 and a conductor 123 connected to the conductor 109. As shown, the conductor- 118 is connected at one end to a juncture between resistances 119 and 121 in series with the bleeder resistance 19 and a resistance 122 and is connected at its opposite end to conductor 42 adjacent the positive side of the'tube 39.

The saw tooth voltage generating circuit 112 includes a fixed resistance 126, rated 220,000 ohms, a potentiometer 127, rated 10 megohms, and a condenser 128, rated .5 of a microfarad connected in parallel with the resistances 126 and 127. The circuit 112 is connected across a suitable power supply by a conductor 129 and a conductor 133. The conductor 129 is connected to the bleeder resistance 19 at a point between the resistances 68 and 69, a resistance 131 and the normally open contacts 132 are connected in series in the conductor 129. The conductor 133 is connected to a point between the resistances 119 and 122, a resistance 134, rated 500 ohms, and normally open relay contacts 136 associated with the coil 116 being: connected in series in the conductor 133. A condenser 137'rated 4 microfarads is connected. betweenthe conductor 129 and the conductor 133'.

In operation the anticipator circuit superimposes a pulsating or saw tooth voltage on the amplifier output.

This saw tooth voltage is adapted to periodically effect deenergization of the valve actuation circuit 16 with the subsequent closing of the valve means 8 for increasing periods of time starting a predetermined distance from the end point (the solution in the container attains the desired characteristics) until the end point is finally reached (no more titrant is required to be added to the solution) at which time the valve actuation is de-energized and the valve means 8 closes. The anticipator thus prevents overshooting; that is, the addition of too much titrant to the solution. Thus, in effect the anticipator circuit acts as a throttling control.

Valve actuation circuit The valve actuation circuit includes a thyratron tube 141 connected between the output of the amplifier and an operating coil 142 of the valve means 8 to control the energization of the coil. The filament of the thyratron is connected to a secondary winding 143 of the transformer 23 by conductors 144 and 146. A mid-tap on the winding 143 is connected to the cathode and screen grid of the thyratron by a conductor 147. The cathode and screen grid of the tube are also connected to the output conductor 87 through a conductor 148, a resistance 149 rated .47 megohm, being connected in series in the conductor 148. The resistance 149 is shunted by a condenser 151 rated .1 microfarads.

The plate of the thyratron is biased by alternating current power. To this end the plate of the thyratron is connected to one side of a secondary winding 152 of a transformer 153 by a conductor 154. Normally open timing circuit operated contacts 156 are connected in series with the conductor 154 and normally open contacts 157 of a push button 158 are shunted across the contacts 156. The opposite end of the winding 152 is connected to the cathode of the thyratron by a conductor 159. The coil 142 of the valve means 8 is connected in series in the conductor 159 while a condenser 160, rated 1 microfarad, is in parallel with a lamp 161 and a resistance 162, rated 47,000 ohms, connected across the coil 142 as shown. The grid of the thyratron is connected to the resistance 127 of the saw tooth voltage generator circuit 112 by a conductor 163. The normally closed contacts 164 of the push button 158 are connected in series in the conductor 163. The primary winding 166 of the transformer 163 is connected to an alternating current power supply by conductors 167 and 168.

From the aforegoing it can be seen that alternating current is applied to the cathode and plate of the thyratron through the operating coil 142 of the valve means 8 and that a direct current bias, which is varied by the signal from the amplifier, is applied to the cathode and grid of the thyratron. While a direct current voltage may be utilized to energize the thyratron such a thyratron may be turned on only at a particular grid voltage, it cannot be turned off at a particular grid voltage, such as the case when alternating current power is used.

Timing circuit Means is provided for preventing actuation of the valve actuating circuit 16 a preselected time interval after the end point of the solution has been reached. As shown, this means includes an electronic tube 170 having a type designation 6BA6 and a timing circuit interconnected therewith. The filament of the tube 170 is connected to the opposite ends of a secondary winding 171 of the transformer 153 by conductors 172 and 173. The cathode is connected to a center tap on the transformer winding.171 by a conductor 174 and to a conductor 177 connected to a conductor 109 on the negative side of the power supply. I A resistance 179 and a timing circuit ope'raflted relay coil 178 are connected in series in the conductor 177. A condenser 181, rated 1 microfarad, is connected between the conductor 177 and a conductor 182 connected to the grid of the tube 170. Normally open contacts 183 associated with the valve operating coil 142 are connected in series in a conductor 184 between the cathode and the grid conductor 182. A conductor 185,

having a resistance 186, rated 1 megohm, and a po tentiometer 187, rated 10 megohms, connected in series therein, is connected between the conductor 182 and the conductor 109 as shown.

Stirrer circuit An outlet 191 for a stirrer 200 is connected to alternating current power lines by conductors 192 and 193. Normally open contacts 194 operated by the timing circuit coil 178 are connected in series in the conductor 193. A pilot light 197 is connected across the conductors 167 and 168 by a conductor 198. Normally closed relay contacts 199 operated by the timing circuit coil 178 are connected in series in the conductor 198. An outlet for an external signal or other apparatus (not shown) is shunted across the lamp 197.

Valve means One form of the valve means 8 that may be utilized with this control means is shown in Figs. 2, 3 and 4. In general it includes a mounting plate 211, a flexible hose 212 mounted on the front side of the plate, spring operated means for pinching the hose 212 to prevent the flow of fluid through the hose and solenoid operated means 214 mounted on the opposite side of the plate operable to overcome the spring means and permit the fiow of fluid through the hose. As shown, in the drawings, the fiexible hose 212 is mounted to extend vertically across the front of the plate and project through openings in upper and lower bosses 216 and 217, respectively, projecting outwardly on diametrically opposite sides of a mounting ring 218. The latter is received in an annular recess 219 formed on the front face of the mounting plate 211 and secured in position as by screws as shown.

The hose pinching or clamping means in this embodiment of the invention includes a pair of members 221 and 222 on opposite sides of the hose. The member 222 is in the form of a flexible diaphragm covering a circular aperture 223 in the plate and having its peripheral edges received in the annular groove 219 and secured therein by the annular ring 218. The member 221 is relatively stiff and is fixed at one end to the lower boss 217 as by a bolt 224. At its upper free end the member 221 is formed with an aperture for receiving a shank portion of a thumb screw 226. The member 221 is normally biased away from the mounting plate so that by adjusting the thumb screw 226 the relative position of the member 221 with respect to the mounting plate may be adjusted. Intermediate its ends the member 221 is formed with a U-shaped portion 227 facing toward the mounting plate to engage one side of the hose 212. The purpose of the adjustment of the thumb screw is to permit the U-shaped portion to be forced into engagement with the tube so that it can be squeezed to a preselected size, thereby permitting a desired flow of titrant.

The solenoid 214 is mounted at the rear of the plate 211 and includes the coil 142 and an armature 232. The latter is disposed at the rear ofthe plate 211 and is pivotally mounted on a Z-shaped bracket 233 attached to the rear of the mounting plate 211. A spring 234 acting between the downwardly projecting lug 236 on the bracket 233 and a tab 237 on the lower end of the armature 232 normally urges the armature to its forward position in which a projection 238, mounted on the armature and projecting through the aperture 223 engages the side of the hose opposite to the U-shaped portion 227, through' the diaphragm 222, to1close off the fiowof fluid? through the hose 212. A stop 239 mounted at the rear of the mounting plate 211 limits the forward movement of the armature 232. The coil 142 is mounted on a core 241 projecting forwardly from a leg 242 of an L-shaped bracket 243 extending rearwardly from the mounting plate and supported on the bracket 233. Energization of' coil 142 causes the armature 232 to be'attracted and thereby'move the projection 238 away'from the hose 212 to-open the passageway'in the hose and permit'the titrant to fiow. As shown, the contacts of switch 183 are mounted on spring arms 260 afiixed at one end to the armature 232 and an arm 261' mounted on an insulating block 262 rigidly secured to bracket233 as seen in Figs. 2 and 3.

While there are a number of selector switches utilized in the circuit it is to be understood that if desired the respective switches may be sections of a gang switch op erated by a single control knob 75 or they may have independent control knobs.

Filterand feed back circuits Several filter circuits and feed-back circuits have been incorporated in the control means circuit to eliminate 60 cycle stray power and other alternating current in the system from being amplified and adversely affecting the operation of the titrator. One such filter circuit is connected in the output of the ampliier. Thus, as best seen in Figure- 5 a decoupling resistor 394 is connected in series in the grid lead 163 of the thyratron and the resistance 149 shunted by a condenser 151 decouples the other side of the amplifier output. The capacitors 151 and 251 prevent alternating current pick-up across these resistors.

The resistor 302 shunted with the capacitor 303, connected between the resistor 300 and ground, filters out alternatingcurrent entering the input leads. A capacitor 305 connected between the grid lead 86 of the tube 22 and the plate lead 87 of the tube 22 suppresses alternating current pick-up in the plate circuit of the tube 22 by cancelling it through negative feed-back to the grid of the tube 22.

The resistor 3&0 serves to give negative feed-back from the output to the input of the amplifier for improving direct current stability while the condenser 391 gives much greater negative feed-back for alternating current to suppress alrtenating current amplification. The resistor 84 also provides direct current negative feed-back for adjustment of amplifier gain and stability.

The conductor 79 biases the grid of the tube 22 with a negative bias in the Start position of the selector switch 78 to reduce the plate current during stand-by operation and to keep the thyratron from firing and the valve 8 closed. The conductor 110 throws the grid of the tube 21 minusto protect the tube when the switch 85 is in the Start position. At the same time the circuit containing the resistor 102, the resistor 99, the resistor 96 and. the resistor 108 is open to take load off the power supply, thereby improving the starting operation.

Operation To warm up the control meansthe selector switches 73,

78, 85, 93, 101 and 104 are placed in their Start positions and the control means 12 is connected to an alternating current power source. After a few minutes warm-up period, in which the load is substantially removed from the tubes: 21 and. 22,, the unit is. ready for use. Assume that it is desiredv to titrate with an alkali. Under these conditions'the selector switches 73, 78, 85, 93, 101 and 104 are placed in their Alkali positions, the position shown in Fig. 5. The reference voltage resistances 96 and 107 are adjusted so that a preselected difierential exists between the potential of the cell and the reference voltage. The timing circuit coil 178 is de-energized.

so that the contacts 132between the power supply 18 and the anticipatorcircuit. 112 areopcn. The. coil 142 in the valvev actuation circuit is. de-energized and the normally open contacts 183 in the grid circuit of the tube 170 in the timing circuit are open. To initiate an operation, the push button 158 is depressed opening the contacts 164 in the grid circuit of the thyratron 141 and closing the normally open contacts 157 shunting the contacts 156' valve coil 14-2 to close the normally open contacts 183 inthe gridcircuit of the tube 17% in the timing circuit; This energizes the timing circuit and-effects flow of power to the coil 17S. Energization of the latter closes the associated normally open contacts 132 between the. power supply and the saw tooth voltage generating circuit 1'12.

Concurrently, the contacts'156-inthe plate circuit of the thyratron are closed so as to permit the operator to release the push button 158. The contacts 194 in the stirrer circuit are also closed so asto permit operation of the stirrer and the normally closed contacts 199 are open interrupting the flow of power to the signal lamp 197; The outage of the lamp normally indicates to the operator that a titration process is in operation.

It is to be understood also that under these conditions the oscillator 1'11 periodically efiects opening and closing of the contacts 136 in the saw tooth voltage circuit 112. When the push button 158 is released the contacts 157 move to their normally open position and the normally closed push button contacts 164 move to their closed position to close the grid circuit of the thyratron and thereby impress the composite amplifier output and the pulsating voltage of the saw tooth voltage circuit 112 on to the grid of the thyratron 141. Titrant flows into the solution and is mixed therewith through the action of the stirrer. As the characteristics of the solution change, the input to the amplifier changes accordingly. As the end point of the solution is approached, i. e., the solution is approaching some preselected characteristic, the amplifier output with the superimposed saw tooth voltage thereon is such that the grid voltage of the thyratron is caused to periodically go more negative than a preselected value. When the thyratron goes more negative than the preselected value, the thyratron extinguishes. During these intervals that the thyratron is extinguished the valve coil 142 is de-energized so that the titrant hose 212 is the solution. can be controlled so that the end point is.

not overshot and the correct amount of titrant is posi.- tively added to the solution.

De-energization of the valve. coil 142 opens. the normally open contacts 183 in the timing circuit which releases the latter. At the end of a preselected interval of time, the coil 178 in the timing circuit becomes de-energized opening the contacts 156 in the thyratron plate circuit and thereby prevents operation of the valve actuation circuit until he push button 156 is again depressed. De-energization of the timing circuit coil 178 also opens the contactslJ-i preventing the flow of power to the stirrer and closes the contacts 199 to turn on the signal light 197 to indicate to the operator that the end point hasbeen reached. De-energization of the coil 178 also opens the contacts 132 disconnecting the saw tooth voltage circuit 112 from its'power supply; Should the titration operation be continued before the preset time. for which the timing circuit is set has elapsed, the contact 183 in the timing circuit will be closed upon energization of the valve coil 142 and the timing circuit will be reset immediately. After the timing circuit has operated the thyratron 141 cannot be fired again until the push button 158 is depressed asdescribed hereinbefore.

The operation of the equipment is substantially the same when the selector switches are placed in their f Acid position.

From the foregoing it is evident that this control means provides a definite end to the titration so that the operator does not have to give his attention to this point. Also by utilizing the signal lamp 197 the operator is enabled to tell at a glance at the instrument when the end point has been reached. This permits of more efiicient and greater use of the operators time in a laboratory during a titration operation. The timing circuit positively prohibits any accidental opening of the valve means due to power line transients or mistakes on the operators part in handling'electrodes and the like. The switch arrangement also prevents the valve means from opening or the thyratron from firing during the initial warm-up of the equipment and disconnects the anticipator circuit from the power supply thereby prolonging the life of the tubes and the relay contacts and assuring maximum service life of the components of the apparatus. Another advantage of this control means is that the valve means may be opened at any time for purposes of adjustment without first having to immerse the electrodes in a solution. It also prevents overshooting as the end point of the titration is reached.

I claim:

1. In titration apparatus or the like adapted for use with a cell, the combination of an amplifier circuit having its input adapted to be connected to the cell and having an output, a liquid conduit, a valve means having an open and a closed position connected in said conduit, a coil operable when energized to open the valve means, means normally biasing the valve means to its closed position, means for initially energizing said coil to open said valve means, a circuit means connected between the amplifier and the coil operative to control the energization of the coil, means for continuously applying to said circuit means a voltage from said cell through said amplifier to control said circuit means continuously in response to the voltage of said cell, means for controlling the circuit means to intermittently close the valve means as the cell approaches a preselected voltage to thereby prevent the oversupply of liquid through said conduit into the solution and means operative a preselected interval of time after the cell reaches said preselected voltage to render said circuit means operative to maintain said valve closed.

2. In titration apparatus -or the like adapted for use with a cell disposed in a solution, reference voltage means connected to the cell, an amplifier having its input circuit connected to the cell and the reference voltage means, said amplifier having an output, a liquid conduit, valve means having an open and a closed position including a coil capable upon energization to open the valve means, means normally biasing the valve to its closed position, a circuit including a thyratron interconnected with said coil for energizing the coil when the thyratron fires, means for applying the output from said amplifier to said thyratron, a saw tooth voltage generator connected to the thyratron for applying a saw tooth voltage thereto and operative when the amplifier output voltage is a preselected value to effect periodic extinguishment of the thyratron, whereby the thyratron is intermittently extinguished as the end point of the solution is approached to throttle the valve means to prevent the addition of an oversupply of a liquid to the solution.

3. The combination recited in claim 2 with means responsive to the operation of the thyratron for signaling to the operator that the end point of the solution has been reached.

4. The combination recited in claim 2 with timing circuit means interconnected with the thyratron operative 10 to maintain the thyratron extinguished after a preselected time interval after the end point has been reached.

5. In apparatus for controlling the flow of liquid into a solution in a container, the combination of a conduit for passing the liquid into the container, flow control means for controlling the flow of liquid through the conduit into the container and operative to selectively pass liquid through said conduit into the container or shut off the flow of liquid through said conduit into the container, electrical control means controlling the operation of said flow control means, means continuously responsive to a preselected characteristic of the solution in the container for generating a voltage corresponding to said characteristic of the solution, circuit means for applying to said electrical control means a voltage corresponding to said voltage generated by said solution responsive means to render the operation of said electrical control means responsive to the voltage generated by said solution responsive means, means for generating a cyclically fluctuating voltage, means for applying said fluctuating voltage to said electrical control means along with said voltage corresponding to the voltage generated by said condition responsive means so that the composite voltage applied to said electrical control means is a fluctuating D. C. voltage, said condition responsive means as the end point of the solution is approached generating a changing voltage which causes said electrical control means to operate said flow control means to shut off the flow of liquid through said conduit for successively longer intervals to prevent an oversupply of liquid into the solution beyond the end point of the solution, and said condition responsive means at the end point of the solution generating a voltage which actuates said electrical control means to maintain said flow control means operative to terminate the flow of liquid into the solution.

6. In a titration apparatus, the combination of a conduit for passing liquid into a solution to change a preselected condition of the solution until the end point of the solution is reached at which said condition is at a predetermined value, means responsive to said condition of the solution for generating a voltage, flow control means controlling the flow of said liquid through the conduit into the solution, electrical circuit means controlling the operation of said flow control means and including a thyratron and means responsive to the firing of the thyratron for actuating said flow control means to pass liquid through the conduit into the solution, an A. C. voltage source having a connection to the plate of the thyratron for applying an A. C. voltage to the plate of the thyratron, means connecting said condition responsive means to the grid of the thyratron for applying to said grid a changing voltage corresponding to the changing voltage generated by said condition responsive means as the end point of the solution is approached, and means operative at the end point of the solution and responsive to the extinguishment of the thyratron a predetermined time by the voltage applied to its grid to disconnect the thyratron from said A. C. voltage source to maintain the thyratron extinguished and thereby maintain said flow control means operative to shut off the flow of liquid into the solution.

7. The combination recited in claim 6, wherein there is provided means for generating a cyclically fluctuating voltage, and means for applying said fluctuating voltage to the grid of the thyratron along with said voltage corresponding to the voltage generated by said condition responsive means so that the voltage on the grid of the thyratron is a composite fluctuating D. C. voltage, said condition responsive means as the end point of the solution is approached generating a changing voltage which causes said voltage on the grid of the thyratron to become increasingly negative to intermittently extinguish the thyratron for successively longer intervals to prevent an oversupply of liquid into the solution beyond the end point of the solution.

8. In a titration apparatus or the like adapted for use with a cell arranged to be disposed in a solution, the combination of an amplifier having its input adapted to be connected to the cell and having an output, a liquid conduit, valve means having an open and a closed position connected in said conduit, a coil for opening said valve means and for maintaining said valve means open under the control of said coil, means normally biasing the valve means to its closed position, means including a thyratron arranged to be fired by the output of said amplifier for energizing said coil to open said valve means and to maintain said valve means open as long as the coil remains energized, means for energizing the thyratron by alternating current, and a saw tooth voltage generating means interconnected with the thyratron and amplifier output and operable to elfect periodic swinging of the grid voltage about a preselected negative value when the solution approaches a preselected condition to periodically extinguish the thyratron whereby the valve means closes periodically before the end point of the solution is reached.

9. In an apparatus for controlling the flow of liquid into a solution and for terminating the flow of liquid into the solution when a selected characteristic of the solution has reached a predetermined value, the combination of means controlling the flow of liquid into the solution to vary said characteristic thereof, means for generating a voltage correlative in amplitude with said characteristic of the solution, electro-responsive means actuatable to control operation of the flow control means, means connected to said voltage generating means for applying a control voltage to said electro-responsive means correlative with said generated voltage and of a magnitude such as to actuate said electro-responsive means when the characteristic of the solution differs from said predetermined value and to deactuate said electro-responsive means when said characteristic equals said predetermined value, means for generating a cyclical time varying voltage, and means for superimposing said cyclical voltage on said control voltage to cyclically vary the amplitude thereof and periodically deactuate said electro-responsive means for progressively longer time intervals as said predetermined value of the characteristic of the solution is approached thereby preventing addition of an oversupply of liquid to the solution.

10. The combination of claim 9 including means operable to disable said electro-responsive means to prevent subsequent actuation thereof, timer means controlled by said electro-responsive means for initiating a timing cycle each time the electro-responsive means is deactuated and for operating said disabling means if said electro-responsive means is not actuated within a predetermined time interval after the preceding deactuation thereof.

11. In an apparatus for controlling the flow of liquid into a solution and for terminating the flow of liquid into the solution when a selected characteristic of the solution reaches a predetermined value, the combination of flow control means for selectively establishing or shutting off the flow of liquid into said solution to vary said characteristic thereof, means for generating a voltage correlative in amplitude with said characteristic of the solution, electro-responsive means adapted to be actuated to operate said flow control means to establish flow of liquid into the solution and to operate said flow control means to shut off the flow of liquid in response to deactuation of the electro-responsive means, means connected to said voltage generating means for applying a control voltage to said electro-responsive means correlative with said generated voltage and of a magnitude such as to actuate said electro-responsive means when the solution characteristic diiiers from said predetermined value and to deactuate the electro-responsive means when the characteristic equals said predetermined value, means for generating a cyclical time varying voltage, and means for superimposing said cyclical voltage on said control voltage [0 cyclically vary the amplitude thereof and periodically deactuate said electro-responsive means for progressively longer time intervals as said predetermined characteristic of the solution is approached thereby preventing the addition of an oversupply of liquid to the solution.

12. The combination of claim 11 including switch means controlling operation of said electro-responsive means, electrically operated timer means adapted upon energization thereof to close said switch means and to retain said switch means closed a predetermined time interval after said timer means is de-energized, and means responsive to actuation of said electro-responsive means for energizing said timer means.

13. The combination of claim 12 including indicator means, means controlled by said timer means for operating said indicator means to indicate when said predetermined characteristic of the solution is reached.

References Cited in the file of this patent UNITED STATES PATENTS 1,951,035 Parker Mar. 13, 1934 2,037,844 Wright et al Apr. 21, 1936 2,047,985 Weir July 21, 1936 2,155,358 Cyr Apr. 18, 1939 2,161,453 Busby et a1. June 6, 1939 2,377,363 Noble June 5, 1945 2,530,326 Davis Nov. 14, 1950 2,607,718 Suthard Aug. 19, 1952 

